Optical fiber sensing device and method
According to the present disclosure, there is provided an optical fiber sensing device including: a reference interferometer for producing a predetermined difference in propagation delay time in continuous light; a sensor interferometer including a plurality of Mach-Zehnder interferometers having unilateral optical paths functioning as sensor units; and a signal processing unit for performing signal processing by using a light reception signal I(t) obtained by receiving light transmitting through the sensor interferometer and a reference signal I ref-1 (t) obtained by receiving light transmitting through the reference interferometer, in which the signal processing unit calculates a cross-correlation R j between the light reception signal I(t) and the reference signal I ref-j (t), and detects a change in the j-th sensor unit by using a change in the cross-correlation R j .
1 . An optical fiber sensing device comprising:
a light source for outputting continuous light;
an optical coupler for branching the continuous light;
a reference interferometer, into which continuous light branched by the optical coupler is injected, for producing a predetermined difference τ ref in propagation delay time in the continuous light;
a sensor interferometer, into which continuous light branched by the optical coupler is injected, including a plurality of connected Mach-Zehnder interferometers for producing, in the continuous light, differences in propagation delay time that correspond to integer multiples of the predetermined difference τ ref in propagation delay time and are different from each other, the Mach-Zehnder interferometers having unilateral optical paths functioning as sensor units; and
a signal processing unit for performing signal processing by using a light reception signal I(t) which is obtained by receiving light transmitting through the sensor interferometer and a reference signal I ref-1 ( t ) which is obtained by receiving light transmitting through the reference interferometer,
wherein the signal processing unit
calculates a reference signal I ref-j (t) corresponding to a j-th (j is a natural number) sensor unit of the sensor units by using the reference signal I ref-1 ( t ),
calculates a cross-correlation R j between the light reception signal I(t) and the reference signal I ref-j (t), and
detects a change in the j-th sensor unit by using a change in the cross-correlation R j .
2 . The optical fiber sensing device according to claim 1 ,
wherein the signal processing unit
calculates a phase X 1 ( t ) of the continuous light at the predetermined difference τref in propagation delay time by using the reference signal I ref-1 ( t ),
calculates, on condition that the difference in propagation delay time of the j-th sensor unit is Mj times τref, a phase X Mj (t) corresponding to the j-th sensor unit by summing up M j waveforms obtained by shifting X 1 ( t ) by τref, and
calculates the reference signal I ref-j (t) corresponding to the j-th sensor unit by using the phase X Mj (t).
3 . The optical fiber sensing device according to claim 2 ,
wherein the signal processing unit
calculates, as the reference signal I ref-j (t), a cosine wave having the phase X Mj (t) as a phase component, and
calculates the cross-correlation R j between the light reception signal I(t) and the reference signal I ref-j (t) by using the cosine wave.
4 . The optical fiber sensing device according to claim 1 ,
wherein the predetermined difference τ ref in propagation delay time of the reference interferometer is longer than a coherence time of the continuous light.
5 . The optical fiber sensing device according to claim 1 ,
wherein the sensor interferometer includes a plurality of Mach-Zehnder interferometers connected in series,
the sensor units are unilateral optical paths in the Mach-Zehnder interferometers, and
differences in propagation delay time of the sensor units included in the plurality of Mach-Zehnder interferometers are different from each other.
6 . The optical fiber sensing device according to claim 1 ,
wherein the sensor interferometer includes a plurality of sensor units connected in parallel, and
a propagation delay time of the continuous light transmitting through the sensor interferometer is different for each of the sensor units.
7 . The optical fiber sensing device according to claim 1 ,
wherein the change in the sensor unit is a change in temperature or distortion of the j-th sensor unit.
8 . An optical fiber sensing method comprising:
branching continuous light from a light source;
injecting the branched continuous light into a reference interferometer producing a predetermined difference τ ref in propagation delay time in the continuous light;
injecting the branched continuous light into a sensor interferometer, including a plurality of connected Mach-Zehnder interferometers, producing, in the continuous light, differences in propagation delay time that correspond to integer multiples of the predetermined difference τ ref in propagation delay time and are different from each other, the Mach-Zehnder interferometers having unilateral optical paths functioning as sensor units; and
detecting, by a signal processing unit, a change in the sensor units by using a light reception signal I(t) which is obtained by receiving light transmitting through the sensor interferometer and a reference signal I ref-1 ( t ) which is obtained by receiving light transmitting through the reference interferometer,
wherein the signal processing unit
calculates a reference signal I ref-j (t) corresponding to a j-th sensor unit by using the reference signal I ref-1 ( t ),
calculates a cross-correlation R j between the light reception signal I(t) and the reference signal I ref-j (t), and
detects a change in the j-th sensor unit by using a change in the cross-correlation R j .